Given a set of lightpath connection requests in an all-optical wavelength division multiplexed (DWDM) network, lightpaths are designed and the wavelength channels are assigned so that the scheme minimizes on average the blocking of existing and provisional requests. This paper proposes a routing and wavelength assignment scheme for DWDM long-haul optical networks that includes routing, assignment and reservation of different wavelength channels operating under the G-MPLS environment. The modeling is implemented under the framework of an object-oriented modeling platform OMNeT++. Network performance tests are evaluated for a long-haul terrestrial fiber network composed of 12 gigaPoPs with an average degree of 3. Traffic blocking of lightpath requests are examined with the average link utilization in the network employing variable number of wavelength channels. Two principal algorithm for wavelength assignments, the first-fit and random types, are studied and proven that the random scheme offers significant better performance than that of its counterpart.